1. Field of Invention
The present invention relates to probes and sensory guides for robot-actuated tools, such as grippers, welding heads, positioning, metering and counting devices, etc., that perform a control function without physically contacting the workpiece being sensed.
2. Description of the Prior Art
Systems are well known wherein sensing devices locate a workpiece or zone (work), and effect relative positioning between the work and a tool for performing an operation thereon, by comparative intelligence that is translated into a control function by which optimum relative positioning is sought to be achieved and maintained. Probes that physically contact the work and follow its contours to cause a tool to track through mechanical (including hydraulic and fluid) and electrical (including magnetic and electronic) linkages, are distinguished from contactless probes of present concern. The Zeewy et al. U.S. Pat. No. 3,883,956, exemplifies such physical probes as applied to a welding operation. A downwardly-biased finger probes the groove or joint to be welded. During relative movement between finger and groove, variations in the latter cause the finger to move, which produces voltages that are translated into movement of the responding welding torch in a duplicate pattern that, ideally, tracks the groove being welded. Such systems are marked by significant disadvantages: finger probes deteriorate due to weld-spatter, and intense heat, consequent upon proximity to the welding zone. More remote spacing greatly increases the complexity and cost of such systems when designed to offset the aggravated geometric problems. Good practice dictates, therefore, that the probe be positioned as closely as possible to the tool, in a lead or advance location to the latter relative to the work, to minimize tracking errors without deleterious exposure to itself, or interference with the tool in performing the work to be done. Contactless probes commend themselves as best suited to achieve these ends.
Many forms of contactless probes are known to the prior art. Among these is the optical approach disclosed by Stanley, U.S. Pat. No. 3,009,049, employing a television monitor in a welding operation, which is subject to disadvantages of damage to the optical system from heat and spatter, as well as aberrations arising from flickering of the welding arc, glowing of the molten metal, and obscuration by flux in the seam ahead of the torch. These variables exact much sophistication to interpret correctly the work conditions, and to implement the necessary controls in the performance of the work to be done, so as to reduce the usefulness of such optical sensors to the simplest applications.
In another welding adaptation, Sullivan, U.S. Pat. No. 3,480,756, employs magnetic sensors to position a welding head with respect to a seam to be welded between which relative movement occurs. Magnetic systems lack the precision and general range of usefulness of the optical sensors, being, as they are, limited to certain magnetic materials, usually ferrous welding operations, being insensitive to small or sudden changes in the welding path unless too close to the heat of the torch to preserve the probe's integrity, or so close as to interfere with the welding itself.
In my prior pending application, Ser. No. 11,176, filed Feb. 12, 1979, for "Wavicle Probe", there is disclosed a probe that guides a welding torch through ultrasonic signals beamed at the joint to be welded, the echoes from which are translated into an electric signal to which robot means for controlling the welding torch responds to cause the latter to track the welding path without physical contact with the workpiece. This is, essentially, an acoustical method for producing an echo in which the elapsed time between sending the acoustic signal, and the reception of its echo, is compared with a pre-selected standard, and torch controls are made to respond to comparative differences thus detected. My prior application defines "wavicle" as "a short burst of ultrasonic signal travelling as a substantially discrete package through the space intervening between the transmitting means and the target surface." (Page 6, lines 4-7.) "Ultrasonic" is then defined as "frequencies of a sonic nature, but above normal human hearing range: generally, this range encompasses frequencies above about 20 kilohertz (KHz), and preferably above about 50 kilohertz (KHz)." (Page 6, lines 12-14.)
While ultrasonic echo devices exemplified by my earlier wavicle, contactless probe inventions, as disclosed in said patent application, identified above, afford many advantages over other prior art devices, some of which devices are discussed above, certain disadvantages have been revealed therein as well. Among these are limited accuracy, and sensitivity to extraneous noises. The limitation on accuracy is, in part, due to the characteristic in such an acoustical system, by definition, to detect acoustical waves that lie beyond an initial oscillatory cycle, thus, introducing uncertainty and the possibility of error up to one wavelength. The first cycle received starts from zero amplitude, with considerable interference from extraneous noise, and increases in amplitude within the next few cycles, with the result that the accurate location of any point on the first cycle is obscured. This problem can not be solved through the use of higher frequencies, due to the fact that the ambient atmosphere readily absorbs frequencies not greatly exceeding 100 KHz.